1. Field of the Invention
This invention relates generally to sleeping bags, and more particularly, a modular sleeping bag featuring a bag-in-a-bag construction for bivouac use such as during camping, hiking, backpacking or the like.
2. Background of the Invention
Sleeping bags are critically important to those adventurous souls who choose to or have been chosen to spend nights in untamed parts of the world. Whether one is a novice backpacker, or an experienced outdoors-person, a principal objective while camping is to keep warm during cold nights, especially during unexpected periods of extreme cold or freezing rain.
It is well known that overnight temperatures vary widely depending upon the particular season, geographic location, terrain, weather condition, and so forth. A sleeping bag capable of providing different degrees of thermal protection in response to these variations would therefore be particularly advantageous. Moreover, because of the varied degrees of metabolic rate of different users, adjustment of the thermal protection levels of a sleeping bag would also be desirable even when the users are faced with the same ambient temperature.
Conventional sleeping bags offer passive thermal protection by providing a layer of thermal insulating materials. Although varied degrees of thermal protection might be achieved by varying the thermal insulation quality and the thickness of the insulating layer, such sleeping bags generally include only a single insulating layer of constant thickness and uniform thermal insulating property. Consequently, a user may find a sleeping bag too warm or too cold as the ambient temperature changes from one night to the next. A user may thus need to bring along a number of sleeping bags for a particular trip. Such a solution is highly undesirable in terms of a user's limited resources, cargo space or handling ability.
Various attempts have been made to overcome the problem of constructing a sleeping bag that provides thermal protection over a wide range of temperature. For example, U.S. Pat. No. 3,584,323 to Worley teaches a construction of a sleeping bag that is convertible into a single sleeping bag, or two sleeping bags. The disclosed construction requires the attachment of two smaller blankets to a large blanket thus forming two "pockets" or sleeping bags on the large blanket. A user may choose to fold the large blanket along its centerline to form one sleeping bag having double layers of blankets. Alternatively, the user may form a pair of sleeping bags by unfolding and laying flat the large blanket, i.e., the outer layer of the single sleeping bag. Slide-type fasteners such, for example, as zippers are disclosed for fastening the edges of the large blanket to form a sleeping bag. Therefore, with this sleeping bag construction, a user may have either a single or double layer of thermal insulation.
U.S. Pat. No. 4,888,828 to Tatsuno discloses a sleeping bag having only a "head opening" for entering and exiting the bag, and a plurality of elastic bands spaced apart and along the length of the bag. The elastic bands constrict the cross-sectional areas of a bag and thus restrain the relative movement of the bag(s) and the user. This patent teaches that an inner bag can be placed within an outer bag. The inner bag is held in place by friction generated by the elastic bands. Therefore, a user may afford varied temperature protection by varying the layer of inner bags.
U.S. Pat. No. 5,005,235 to Huang discloses the construction of a two-person modular sleeping bag. The two-person sleeping bag is formed by unfolding and laying flat two one-person sleeping bags, then superimposing one unfolded bag over another, and fastening the top unfolded bag to the bottom unfolded bag by means of zippers. The Huang patent also teaches the insertion or removal of thermal insulating pads into or out of a compartment formed along a side of a sleeping bag so as to accommodate usages in fall or winter.
A disadvantage of the aforementioned sleeping bags is that they fail to provide variable thermal protection and a fail-safe feature for closing an open side of a sleeping bag.